Why am I being asked to review and add transactions that already exist and have, in fact, been reconciled?

Welcome to the QuickBooks Community, @usercelticcrests.

Does this happen when creating a transaction in QuickBooks? If so, let's make sure that you will input different details such as ref. no, when entering and saving a new transaction. For your reference, see this link: Transaction already exists - save anyway?

Let's also determine if this is a browser issue. To begin, access your QBO account using a private mode. The following are the shortcut keys you can use:

• Google Chrome: press Ctrl + Shift + N 
• Mozilla Firefox and Microsoft Edge: press Ctrl + Shift + P
• Safari: press Command + Shift + N

Once logged in, do what you did again before seeing the message. If this works, go back to your regular browser and clear the cache. This will remove the stored cache or cookies to refresh your browser. If the same thing happens, use another supported browser. It could be that the one you're currently using has a temporary issue with QuickBooks. 

If the issue persists, I recommend reaching out to our technical support team. They use specific tools to do a screen share so they can further investigate the root cause of the issue. Here's how:

1. At the top right, click the Help icon.
2. Select Contact Us.
3. Under What can we help you with, enter a brief description of your concern.
4. Click Continue.
5. You'll be routed into the Choose a way to connect with us page.
6. Choose either Chat with us or Have us call you.

Then, to help you ensure that your transactions are properly accounted for, you can visit the Categorize and match online bank transactions page for the detailed guide.

Feel free to get back here if you have further concerns about accessing your QBO account. I'll be around to help you in any way I can. Have a good one.